Gas viscosity responsive apparatus



April 1954 J..C. WESTMORELAND GAS vrscosrry RESPONSIVE APPARATUS Filed July 9, 1952 lll' l wi l}:

INVENTOR Juuus-C. \"/Es TMORELA ND ATTORNEY Patented Apr. 6, 1954 UNI-TED sures 7 Claims;

' This invention relates to a deti'ic'e for measur ingfthe'ratebf gas flovv'fthrough a capillary tube asfafie'cted by the viscosity of the 'gas The" accurate measurement and regulation ofisr'n'all Y gas flows is required in a known method ofmeas- 5 ufin'g the visr'zosity of a gas; which makes use otjthe classical equation of Poiseuille for emiress mg the jfiow" of a fluid throughacabillary tube. In its'si'mples't form'this equation is z ll) '5 "PR4 1 m where 7 mm.) :r'aaiii "of the tube- L (cm.)= length of. the tube" is h" (gm.-/cm J-see. =pressure 'dioiffrom' inlet to outlet Qr'the tube a. .4 Q'- (emg f/sec'l volum me of fiow' atmid-sectio'n f i l l r u (pdi S) =ViSCOSity of the gas in The term ig!v 8L is" constant for any 115 tube ianl' therefore the as variables, under conditions of constantftempera-T e i h ssu dr w aniiifi e istas By'keping h constant and accurate :measuringf the rate of "fiowi of the gas in the capillary tube; it "is possible to-obtaiii 'a mea-s'urment of they, viscosity. Attempts have been made with some succes's"- to: utilize-the above rel'ationshib in determining viscosity-by "measuring the rate of flow 'of' the found exceedingly diificult' to nrlain't'ain the "head or ressure ''clifierential" between the "ends of f the cab'illary"tube' 'sulfici'ently constant to" permit the desired accuracy of measurement. It must b'kept inmind-that the total pressure drop 111 :1!- volved is in the order 'of'a fewinches of "mercury andtha't thereforethe rate of'flow in the capillary tube'is greatly affected by relatively small changes: in'the' absolute valueof the head; It'jhasbeen necessary, with the prior 'art' methods of'whicli 45 I 'amaware, to spend'hours in maRinga' deter-J mination of viscosity for a'singlegas samplefand' the final accuracy has been in the order of $1.0 L This has been largely due'to' the necessity for making repeated" measurements and averagingout-,theresults due to the large? possible instantai-i" neous= deviationz-from the mean value-'of' the" measurement taken. 7 y Y v My invention-provides a capillary-tube gas iflo'w system'wherein-"the factors are maintained? con- 5 stant to such a degree that it is possible to deter-r mine the" 'viscositybfiaf igas 'sariipl less the t niinutesfjirfthe'case of airat stan ard temp ture'and pressure, hi? to :approkunately t ee Inin'titesinthe case of helium, andfthe 'rsultsf haye beeneonsistentlyaceu fateto within i'plb Furthermore," theya 's r ct'ors'afiect e t measurement are mal ine'c' l soiconstant an I instantaneous dev'iat ns sofsmall that itTis e5 b o a ea u th n n r te "o g 'as directly and continuouslywith sufliciefitacciir c5" for many purposes. v a I; H The accurate and rapileqetrminatidn of'fv' cosity is" not only a matter of great" scie c, interest? but has become j run'creasmg practical importance 'with the 'deifrelbbrfi I extremely long gas"1mes"i fco nee accurate measuremenr'a ddeter v n I flow of gas through suchfnnes r, It sffal'so" of interest i con ection with" the study 0:111 v speed flight in the atmosphere; 7 The "mea ment of gas flowafihigntember'atu s hampered by lack of suitabletechfiiques oiim uring viscbsityjin the temperature region be'tw F- a .d 5 0i b m3! mP PY QfiPWT PW emp r tu e .diree y'ini s em fi'aiie iit e'jmns el wthatb ili a lys ta le b efl r yl' r e' the m mel tie mea e eause' r ei ab li ix ea ur l ael e With tan t t ber turee 1011s I f I f.l' 1.*a -i,... r pr ,o y. i ent fi'ie. fr rtic l ll well ad" pteril t'o the aqcura e easfiremmor gas viswsity a v r= sh.- eS e It is accordingly an ob'jectofmy inventiofito" provide an improveaj'apeamms "for rapidly ar'id accurately measuring "mew/recast? of gases. m

It is a further object of my inientiofito'broyigle a-noyelfapparatusfoi"instantaneously' mea "'rjm the visdb'sitybfagas from-a sman sa'fifiil st tue gas. 1 Another object is to accurately measure ele vated temperatures as a function of the "chem of viscosity with temperatui'el Still-another object is' toiprbvide; in an abpa ratus for! measuring 'the' flowof a -very sniall yol um'e of a i gas; ndv'el' and*:=improved" means for maintaining a very constant gas pressure ferential'.:" 1 r r t V. t. Another object is to pro'vide forzith accurates measurement of -gas viscosity-at very" high-:-'-pres-' suresxu. a I k The specific nature of the invention, as well 3 as other objects and advantages thereof, will clearly appear from a description of a preferred embodiment as shown in the accompanying drawing in which:

Fig. 1 is a diagrammatic view, partly in section, of an apparatus embodying my invention;

Fig. 2 is a plan view, on an enlarged scale, of the float valve; and

Fig. 3 is a diagrammatic view of a modification of the invention for measuring the instantaneous rate of flow.

Referring to Fig. l, l is a nipple to which is connected a source of the gas which is to be tested, 2 is a valve for controlling the flow of this gas into the apparatus, 4 is a reservoir normally nearly full of mercury, 6 and connected by a tube 1 to a float chamber 9 having a thick top closure ll provided with a passageway l3 which provides a continuation of tube 1 and leads into passage which connects to volume chamber Hiv on top and is bevelled at the bottom at about 60 to form a seat for the coned point 18 of .a float valve '20. Valve 20 has a number of perforations drilled in it at 22 leading to a bottom aperture 26 whereby any mercury which flows from passage 15 past the valve falls by gravity through the perforations 22 into the bottom of float chamber 9 and collects at 26. It will be apparent, that when the mercury has risen to a certain level, the float valve 20 will rise to a point where the needle valve seat 2| shuts ofl further flow. The float cham-ber, float and valve are made of methyl methacrylate resin, commonly sold as Lucite. It has been found that a Lucite valve and valve seat are not eroded by the flowing mercury, whereas a steel valve is eroded. Moreover, the mercury remains clean in contact with the Lucite.

Volume chamber 28 is connected to volume chamber l6, and a pressure equalization tube 30 leads from the top of chamber 28 to the top of the float chamber 9 as well as to the top of capillary tube 32 and also to a nipple 14 for connection to a vacuum pump (not shown),

this last connection being controlled by cock l0.

From the bottom of float chamber 9 a tube 34, inwhich flow can be controlled by cock [2, leads to the top of reservoir 4. A differential pressure gauge 36 may be connected across the capillary tube 32 to indicate the diiierence in pressure between the ends of the tube.

The volume chamber has two sections, l6 and 28, which are made of glass with a necked section between the two and at the base of the lower. Platinum contact wires, 38, 4'0 and 42 are sealed into these neck sections, and the top of the upper bulb 28. These wires are bent downward to give sharp break signals. The primary purpose of the necked sections is to have a small cross-sectional area at the plane of the contact break.

Contact wires 40 and 42 lead to a conventional electric timer 44 and. are so arranged that when the level of mercury in chamber it falls sufliciently to break contact with the wire 40, the timer is started, and when the mercury has fallen so that it breaks contact with wire 42, the timer stops, giving an accurate indication of the time to displace the volume of mercury between these two levels with the gas being measured. This volume can be easily and accurately determined by weighing the amount of mercury'which is so displaced. Contact wire 38 is connected'to a signal lamp 46 which lights when it is contacted by the mercury in chamber 28, giving a signal to indicate that chamber 28 is full and the apparatus is ready for the beginning of a test run.

The operation of the above apparatus will now be described.

The first step in preparing the apparatus for use is to determine the volume of the chamber 16 between contact points 40 and 42. This may be done very conveniently before the volume chamber unit i6 is joined to the float chamber 9. Also, while not essential, it may prove convenient later on to know the volume of chamber 28 between contact points 38 and 40, and its determination at this time involves very little extra work.

To determine the volumes of the chambers, they are filled with mercury from an auxiliary reservoir, then the mercury is withdrawn. As the mercury surface in the volume chamber breaks from contact 28 (or 40) the discharge is diverted into a weighing flask. As the mercury surface breaks from contact 40 (or 42) the flow is stopped. From the weight and temperature of the mercury collected, the volume is calculated.

In making this volume calibration, it is necessary to always have the mercury surface falling when the observations or setting are taken at the contact points. The primary reason for this is that this is the direction in which the mercury surface will be moving when the apparatus is in use. For indicating when the mercury surface breaks from the contact both visual observations and an electric continuity meter have been used.

Next, the several parts of the apparatus are assembled, using suitable cements. After assembling, the apparatus is washed with dilute nitric acid, thoroughly rinsed with distilled water and then with alcohol, and dried. Finally the reservoir is filled with slightly more than enough mercury to fill both chambers 16 and 28 and the base of the float chamber. The apparatus is now ready for use.

It is appropriate to mention that the materials of construction and method of assembly described above are suitable for use under gas pressures (absolute), ranging from a few millimeters of mercury to about two atmospheres.

Modifications which will permit the apparatus to be used under higher pressures will be discussed later.

Referring to Fig. 1, with all of the mercury in the reservoir 4, valve 2 is closed and cocks 8, l0, and i 2 open, a high vacuum pump is connected at l4 and the entire unit is purged of all gas as completely as possible. Then cocks l0 and ii! are closed and the gas sample inlet valve 2 is opened. This must be done with some care since the rate of pressure increase in 4 must not be too rapid, and yet it must be at a much greater rate than gas will flow through the capillary tube.

the float valve. mercury will first fill the float chamber enough to close the float valve, and thereafter will within reservoir 4 has reached the desired value,

when valve 2 is closed.

Before starting a measurement or run, a sumcient time interval must elapse for pressure con- This will cause the mercury to rise through the tube 1 into the passage above 7 Since cock i2 is closed, the Y i ditionsto equalizethrou'ghout the systems The following col'iditiol'is then' exist z Cocks l2 and 8-are closed; I hemercury' 'in the float chamber has:raised:the float so= that the: valve point 18-:

is pressed 'firmly enough a'gainst' its seat thatn'o m'ercury can now from I fi into lli The gas pressure is the: sameine reservoir 4',- the: float: chamber 9 and the top of chamber 28.

To -place the app'aratus in operation',- cock l2 isopeneds- The set otcond-itions-swhich will be 10? established when a' steady rate of flow-is reached are-: The -outflow 0t mercury from pool 26 will lower the float and valve admitting-mercury tronr chamber l6 into float chamber 9. Since-this infloat and valve will 'be ra-ised, choking dOwll -ithe rate' of inflowl Due to the: pressure equalizing tube;- 30a the gas -pressure in the upper: part of the: valve: chamber s -will: b'e' the same as: thatabove theamercurydnchaniberL28. I The h'ead h producingthe-flow isequal tothe vertical :height; from 1. the surfaceof the mercury their-- float chamber to thecutflow point of the tube 34 below 'valv'e l2. 7 This may 'be determined by the use ofia cathetometeror by adifierential-manometer or? a..- pressure gauge 3 6 connectedlebetween the capillary tube terminals, as showns.

In order 1 that thesaboveconditions maybe attainedntisnecessarythat .thepassage from .float end;.shall bezvery smalh Insome apparatus the; lower part ofithis:- .tu'ber: has been. made so small. that,-'...with -a: trap. atL-thel end; only one .or two drops;.of..mercury emerged .fronrthe trap. per: second;-. That-.thetheig ht fronr the mercury. surface: imthe:float-.chamberx:to-the tube outlet is equal to the r. pressure drop across: the capillary tubeihas :been established by. manypairs of measurements:.-.. However; it should be noted that this holds only; when. cock-l2 isuwide open.:. If,v as inssome models, .coclr l 2: is. replacedsby a. needle valve, and the rate-oiithe mercury-.flowisreguelated: by .=this valve, the equality between. the height of the mercury passage and the pressure drop willnot obtain. Itwill then becomenecessary. tocuse'a manometer across the capillary." tube;

Again; ithasv been. found that there is no: hunting? action of the floatvalve in vmaintaining the rate .of outflow fromchamber. l6 equal :to thatrfrom float chamber 9. However, theflow through the-float .valvemust be in. the laminar region.

0 Since the-.gas pressurein the float chamber is the sameas that above the mercury in chambers l 6;;28,1-theupressure or. force of a the mercury upon theiprojected area of the point of the valvewill. vary, withtheheightof the mercury in- IS, 28. The opposing force exertedby the valveis derived-from. the buoyant action of the. mercury upon the float. As. this force must be greater when. l6,'1.28' are full than when nearly empty, it follows that the depth of the mercury in float. chamber 9"will.be greater at thestart than at the end .ofia run... Calculations have shown that this change-in .depth is very small, .about 0.0014 cm. In themodel .towhich this value applies, this. would. be equivalentto a. decrease in h of less than, 0101 In thisitype ofoperation the rate of flow of the mercury, at equilibrium, will be. determined by, the quantity of gas that'the pressure differential "h'can force through the capillary restriction" .32" att'est conditions,- If' the. capillary 32" were'blo'ck'edi thennogas could "enter the meter-' chamberutmreservoir. d especially. at. the: outlet i 6;? nag-chamber"anurtherewouldibeno mercury fiow into -the chamber' l; Ah ydrostati'c balanw'wouldii then" exist where the gas-pressure (PE) in" the: chamber-4 =less the pressurei(P129 in'zthe measur ing chamberl 6;" 28rand the float chamberifi woul be equal to the value of the mercury 'column --7i condition represents the: zeroflowpoint, above which :flow ratesi may be obtained o'v'e'r a range governed by the'cross section and: shape 01 the discharge section of the mercury passage? Beyond: this range the: condition of hydrostatic baIanceEcanranQJongerzbe said t'o 'ex ist and pres sure losses the discharge section'-- are of ai magnitude where-' they: must i be takeninto ac:- coun-t-I In place 'of an'on-ofi valve, a --regulating valve may be used for I 2 In thiscaseytheoutflow tubw should be of uniform size throughout. Also? the vertical dis'tance representedby h in Fig; 1, would-, ri'o't be a measure of the pressure drop across the capillary tube. This pressure drop" would now have to be .measured with a manometer Operation of the meter with this type :of a valve h'as been called restricted operation.

It was -men'tioned that withthe type of con struction' described', the maximum pressur'e at which the apparatuscan be'used with safety, is about 2 atmospheres, absolute; One method' for overcoming this limitation isto' place-the a paratus within a suitable pressure chamber; This necessitatespressure connections into the "enclos in'g chamber as well as electrical conne'ction's' -for=- the signaling contacts Also-some provisionmust made for operating the cocks a and n ce:

o rin):

the connecting lines to them may be brou'glit outside.

A11 alternative procedure to the' above -is to make the volumechamb'e'rsi 8; Hi; the float cham her 9 and the reservoir 4 of steel.

Since the viscosity of a gas changes rapidlywith a change of temperature; one of these apparatuses may be used for temperature measurements; Forsuch use; the capillary' tubewould be coiled into a 'compact sensingunit; The=unit wouldbe charged once for=all"with a suitable gas. The time interval will be ameas1-1re' of theaverage relative temperature, or actual tem' pera-ture after a calibration has been=made, over= the -time interval.

Insuch an arrangement and use "as here-suggested, someform of'pump may be'used for trans-- ferringv the-mercury from thereser'voi'r" to the" measuring chamber; orthismay-be done gravi'-- metrically-by inverting: the unit.

The-apparatus maybe'mo'difiedso'a'sj to "indi catethe" rate of flow of a gas sample:- This modification, which is shown" schematically" in Fig. 3; is made" by replacing the chamber unit l6, 28, with a uniform boretube 5W. Theron-- tact points'arereplaced"by"a fineplatinum re-.

sistance wire '52 mounted along the" axis of the" tube; The ends of this wire" arewonnectd. tothe primary winding-of aniron core'transformert Man d suppIied from a source 'offD." C; current 56. As the'mercury surfaceifalls, the resistance;

in the'circuit'increaseswith a correspondingjdrop? in the primary current and I degree" of. ma'gn'eti z'a'tion of. the primary winding; This iridi'iceseii'iv emf in" the secondary. winding; the strength of primary. This secondary. winding voltage may; be 'obtained'with a. suitabletype of"voltmeter 611 and 'byjcalibration; the volume rate of*me'rcuryjflowandbf the gasalso; may be read'dii rectly from 'the'volt meter.

bbviously, this arrangement can be combined with the temperature sensing element mentioned above. .In this case the voltmeter could be calibrated to indicate temperature, since the rate would vary proportionally with the temperature of the gas.

A temperature measuring device constructed as indicated above has one unique advantage. By making the capillary tube 32 of metal or metallic alloy which can withstand high temperatures for an appreciable time, accurate temperature measurements can be made even in a temperature range so high that the tube walls are breaking down during the measurement. As long as the inside of the tube remains intact, the measurement will still be accurate. This is not true of other types of temperature sensing elements, e. g., a resistance wire, since as soon as the wire begins to decompose or erode due to the high temperature, resistance measurements taken as an indication of the temperature will no longer be accurate. Thus, by making the apparatus, which uses very little metal, easily replaceable and connecting it to nipples of highly refractory, thick walled material, it will be apparent that accurate direct temperature measurements can be taken in a region and under conditions very diflicult to measure by any other means.

In practice, it has been found that the apparatus described maintains the pressure differential across the capillary tube at a remarkably constant level, which is believed to account for the high degree of repeatability and accuracy obtained. It will be noted that once the system is stabilized, there is no appreciable hunting action whatever. The float valve apparently acts as a highly damping resistance element and lets in the mercury in very small, very uniform increments which permits it to vary by only a small fraction of one percent, thus preventing the building up of pressure oscillations which would otherwise tend to occur in the closed gas circuit, with resultant large deviations of instantaneous pressure and impairment of accuracy.

It will be noted that the tube 34 is made of sufliciently small diameter so that if the pressure in reservoir 4 is the same as in tube 30, the mercury will remain in the tube despite the opening at the bottom of the tube, and, the system will remain hydrostatically balanced. However, even if the tube 34 is made sufliciently large so that leakage from the tube cannot be prevented, this will not necessarily afiect the operation of the system shown in Fig. 1, as long as the flow in the capillary 32 is not less than the leakage from tube 34 for under these conditions float valve 20 will still need to operate to admit even more mercury than is leaking and the tube 34 will remain full of mercury.

A particular advantage of the arrangement shown is that the reservoir 4 acts also as a filter to trap any impurities or mercury compounds which may form. These impurities will float on the surface of the mercury 6 in the reservoir and since mercury is withdrawn from the bottom of 6, the impurities will not get into the valve system and so can do little harm.

' The system described maintains the rate of flow of mercury constantly regardless of the quantity of mercury remaining in the chamber above. As mercury leaves the chamber i6, 28. it is replaced by an equal volume of gas flowing from the capillary tube 32. The pressure head creating the gas flow is equal to the vertical distance from the surface of the mercury in the float chamber 9 to the bottom outlet of the tube 34.

The timer 44 shows how long it takes for the volume of gas (at this pressure difierential) between 40 and 42 to flow through capillary tube 32. From the volume represented between contacts 40 and 42 the rate of flow, Q in Poiseuilles formula, may be computed, and this in turn readily gives viscosity.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of my invention as definedreservoir, a gas conduit connecting the top of said chamber to the other end or said capillary tube for receiving gas thererrom, a quantity of liquid of greater density than the gas being tested in said displacement chamber, a float chamber between said displacement chamber and said reservoir, a conduit for admitting liquid from the displacement chamber to said float chamber by gravity flow, a liquid conduit between the bottom of said float chamber and'the top of said reservoir, a float valve in said float chamber for metering the .rate of liquid flow from said displacement chamber to said reservoir, a gas pressure equalizing conduit from the top of said displacement chamber to the top of said float cham-.-

ber, and means responslve to the rate at which liquid passes from said displacement chamber to said reservoir, said gas and liquid reservoir having at least suificient capacity to hold all of the liquid in the system at one time.

2. Means ior maintaining a constant gas pressure comprising a gas and liquid reservoir, a gas outlet aperture in the upper portion of said reservoir, a liquid inlet tube connected to the upper gas containing portion of said reservoir, 2. float valve chamber connected to said tube for controlling supply of liquid to said tube, and a liquid supply chamber connected to said float chamber for supplying liquid thereto, whereby the float chamber is efiective to maintain a constant head of liquid in said liquid inlet tube.

3. The invention according to claim 2, and an enclosed gas system including said float chamber, whereby a gas pressure difference is maintained between gas in the enclosed system and gas in the reservoir, depending on the head of liquid in said liquid inlet tube.

4. Means for determining a function of the viscosity of a gas comprising a closed sy t adapted to contain a quantity of gas to be tested,

said system including a capillary tube, a reser' voir for supplying gas under pressure to the end of said capillary tube, and means for maintaining a constant pressure of said gas in said reservoir comprising a displacement chamber at a higher lever than said reservoir, a quantity of liquid in said displacement chamber, a float chamber at an intermediate level between said displacement chamber and said reservoir, a passage for admitting liquid from said displacement chamber to said float chamber by gravity flow.

a liquid gravity conduit between said float chant-i her and the top of said reservoir said conduit being normally open at the bottom and of sumciently small internal diameter to retain liquid in static balance therein when the pressure at the bottom of said conduit equals the head of the liquid in said conduit, a gas pressure equalizing conduit from the top of said displacement chamber to the top of said float chamber, means for indicating the rate at which liquid passes from said displacement chamber to said reservoir, said reservoir having at least sufficient capacity to hold all of the liquid in the system at one time.

5. The invention according to claim 4 including a valve in the conduit between the bottom of the float chamber and the top of the reservoir said valve being adjustable to restrict the rate of flow of liquid in said conduit.

6. The invention according to claim 4 includ- 19 ing means for transferring liquid within the closed system from the liquid and gas reservoir ,to the displacement chamber.

7. The invention according to claim 6 wherein said last-named means comprises a liquid conduit from the bottom of said reservoir to said displacement chamber, and a shut-oil valve in said conduit.

References Citcdin the file of this patent UNITED STATES PATENTS Number Name Date 1,630,307 Norwood et a1 May 31, 1927 1,884,896 Smith Oct. 25, 1932 OTHER REFERENCES The advanced Treatise on Physical Chemistry, vol. 1, J. R. Partington, pgs. 8'76-881; QD, 453, P3. 

